chore: address Copilot review round 3

- CI now installs a pinned `claude` CLI and runs `claude plugin validate` as its
  own step. The guard skips the authoritative validator when the CLI is absent,
  which without this meant "always, in CI" — so the acceptance criterion was
  aspirational. Verified it needs no authentication (clean HOME).
- skill-eval: classify a run from its terminal `result` event, not its exit
  code. With `--max-turns 1` a run in which a skill FIRES necessarily hits the
  limit and the CLI exits 1 (`error_max_turns`, `num_turns: 2`), so last round's
  blanket nonzero rejection threw away exactly the observations the eval counts.
  A run with no terminal `result`, or an unusable subtype, still rejects.
- skill-eval: fail collection on a skill that does not parse, a model-invoked
  skill with no eval file, unreadable JSON, or invalid cases. Skipping them let
  `skills:eval` exit 0 while silently omitting the skill just broken.
- verify-skills: `main()` takes an optional skills directory, and
  `verify-skills.main.test.mjs` drives it over fixtures — missing SKILL.md,
  malformed frontmatter, undeclared invocation mode, missing/invalid evals,
  budget overflow (and that name-only skills do not count toward it), and
  multi-offender reporting. Matches the sibling guards' *.main.test.mjs
  precedent; without it the gate could stop enforcing while the parser tests
  stayed green.
- issue-create: the note claimed an issue arrives unlabeled, contradicting
  .github/ISSUE_TEMPLATE — blank issues are disabled, the bug form applies
  `bug`, the feature form applies `enhancement` + `v2`. Now a table of what each
  form sets and what triage still has to add.

Signed-off-by: cliffhall <cliff@futurescale.com>

AGENTS.md

@@ -149,7 +149,12 @@ that from happening:
    **malformed YAML**, which loads the body with an *empty* description, so
    `/skill-name` still works and a manual spot check passes while the skill can
    never auto-fire again. An unquoted colon in a description is enough. It also
-   runs `claude plugin validate` when that CLI is on PATH.
+   runs `claude plugin validate` — the authoritative schema — when that CLI is on
+   PATH **and new enough to have the subcommand** (2.1.233+; below that it exits
+   nonzero as an unknown command, which must not fail the gate for someone who
+   simply has not upgraded). Because the guard skips it when absent, CI installs
+   a pinned CLI and runs it as its own step, so "authoritative validation runs in
+   CI" is true rather than aspirational.
    ⚠️ Frontmatter is only read when the opening `---` is the file's **first
    line** — no BOM, no leading blank line.
 2. **Every skill declares its invocation mode explicitly.**